# Formatting a citation to a MathOverflow answer

What's a good way to format a citation to a MathOverflow post in a paper? Here is a first draft (with hyperlink, and assuming it's reference number 16, say), but maybe people can think of improvements:

[16] Pietro Majer, answer of April 8, 2014, 17:26pm HST to MathOverflow question 162724, Smooth convex extensibility of combination of two line segments.

(Related question: does the software know my time zone when it displays the time of day of an answer on screen?)

• I think including the exact time in the reference is completely unnecessary -- note that in references to journal articles, usually only the year is given (and not even the month, let alone the precise day or even time). – Stefan Kohl Apr 16 '14 at 23:21
• I disagree @StefanKohl. The point is to be clear which version of the answere is referenced. However, the example is a bit peculiar as it seems surprising that OP would actually want to quote the first revision as opposed to the current one. – user9072 Apr 16 '14 at 23:24
• @quid: In this case I'd just specify the version number, rather than the time. – Stefan Kohl Apr 16 '14 at 23:26
• I would include a link to the answer too. And possibly to the exact revision if you want to be precise. Like mathoverflow.net/revisions/162826/1 links to what you say (though it is surprising) but mathoverflow.net/revisions/162826/5 is what is the current answer to the question. // Regarding the timezone: the time displayed is UTC, no local timezones are taken into account. – user9072 Apr 16 '14 at 23:28
• @StefanKohl yes, I agree that the current form is a bit surprising and possibly misleading and not what is really meant. Still I felt that the analogy to journals was not a valid analogy. – user9072 Apr 16 '14 at 23:30
• By the way, Stefan and quid, this one of the important issues the discussion - meta.mathoverflow.net/questions/800/… - is trying to solve. – François G. Dorais Apr 17 '14 at 0:45
• I have tried to search for older discussions on tea. If found this and this. – Martin Sleziak Apr 17 '14 at 6:03
• Thanks @quid for the timezone and revisions info. – Bjørn Kjos-Hanssen Apr 17 '14 at 15:58
• Thanks @MartinSleziak for the tea discussion, which includes BiBTeX ideas. – Bjørn Kjos-Hanssen Apr 17 '14 at 15:59
• @Bjørn Be careful with the author field in BiBTeX. See the comment by Emil in this discussion: meta.mathoverflow.net/questions/1002/… – François G. Dorais Apr 17 '14 at 19:45
• Perhaps someone can create a bibtex style @MathOverflow{ etc.} that we can add to our bibtex set-up in such a way that it will be set automatically in a nice way using the bibtex field data that is provided under the "share" button? Right now, the bibtex bbl output I get is not very satisfactory without modification. – Joel David Hamkins Apr 18 '14 at 14:33
• @JoelDavidHamkins: The main issue is with bibtex itself. The most viable option would be to recommend that users switch to biblatex and outputting an @online entry instead of a bibtex @misc entry. – François G. Dorais Apr 19 '14 at 11:50

On the main site, the (nearly invisible) cite button found in the share menu gives an example citation and gives both bibtex and amsref misc entries that are easy to cut and paste.

Unfortunately, the mechanism to generate the bibtex entry has some bugs.

@MISC {22350,
TITLE = {What are some examples of colorful language in serious mathematics  papers?},
AUTHOR = {Fran&#231;ois G. Dorais (http://mathoverflow.net/users/2000/francois-g-dorais)},
HOWPUBLISHED = {MathOverflow},
NOTE = {URL:http://mathoverflow.net/q/22350 (version: 2010-04-23)},
EPRINT = {http://mathoverflow.net/q/22350},
URL = {http://mathoverflow.net/q/22350}
}


To get a proper entry from this:

• First decode any HTML encoded characters. For example, &#231 above should be replaced by ç, {\c c}, or equivalent. If you use special characters like ç, make sure to use the LaTeX package inputenc with the appropriate encoding option (e.g. utf8). Also use bibtex8 since the original bibtex only supports the 7-bit ASCII character set.

• Since bibtex tries to parse the author field and break it into parts (first, last, suffix, etc.), it is best to remove the parenthetical link to the user profile since that will often break the parsing mechanism. (An alternative is to only use the link to the user profile and delete the name, but that might lead to sorting issues.)

• Since this post is an answer rather than a question, consider editing the title to make this clearer. You may also consider changing the URL to http://mathoverflow.net/a/22350.

• Bibtex traditionally only supports YEAR and MONTH of publication, which is unfortunately too coarse for MO posts. Fortunately, many styles do recognize the DATE field; consider adding it. If the post has a nontrivial revision history, you may want to put a date other than the first posting.

• If the bibtex style you use does recognize the EPRINT or URL fields, the visibly redundant entries containing the post URL could result in it being printed two or three times. Consequently, you may have to remove some of these entries to fit your preferred bibtex style.

• If you use the hyperref package, you could also wrap the URL in a \url command in the NOTE field so that it becomes clickable. Do not do this for the URL field since styles that use this field will normally do the wrapping for you. A few styles support the URLDATE field which, combined with URL, is perhaps a better alternative than the given NOTE field.

• The use of the EPRINT field is extremely style dependent. Some styles will do something reasonable with the field given above but many more will not. Maybe there is some style out there that understands EPRINT but not URL. Unless you use that style, it's probably better to remove the EPRINT field.

After all these recommendations, you get something that should work reasonably well with most styles:

@MISC {22350,
TITLE = {What are some examples of colorful language in serious mathematics  papers? (answer)},
AUTHOR = {François G. Dorais},
HOWPUBLISHED = {MathOverflow},
DATE = {2010-04-23},
NOTE = {URL:\url{http://mathoverflow.net/a/22350} (visited on 2014-04-22)},
URL = {http://mathoverflow.net/a/22350},
URLDATE = {2014-04-22},
}


I guess the best advice is to get to know the bibtex style you use and figure out the best way to format a MO bibtex entry for that style. Unfortunately, publishers will often force authors to use peculiar styles. If that's the case, ask the editor to explain how to properly format a MO bibtex entry for that style.

• Another thing not mentioned is that there should be brackets around math in the title, otherwise something like How to prove $A \Rightarrow B$ will render as "How to prove $a \rightarrow b$". The correct value would be How to prove {$A \Rightarrow B$}. (I found this post through math.SE, I cannot edit on meta.MO yet, and it's probably best to keep all the info gathered in one place.) – Najib Idrissi Oct 3 '15 at 15:37

Users of the biblatex package can use an @online entry type. From the biblatex documentation:

online: An online resource. author, editor, and year are omissible in terms of §2.3.2. This entry type is intended for sources such as web sites which are intrinsically online resources. Note that all entry types support the url ﬁeld. For example, when adding an article from an online journal, it may be preferable to use the @article type and its url ﬁeld.

Required ﬁelds: author/editor, title, year/date, url

Optional ﬁelds: subtitle, titleaddon, language, version, note, organization, date, month, year, addendum, pubstate, urldate

Here is a reasonable example:

@online{MO22350,
title = {What are some examples of colorful language in serious mathematics  papers?},
author = {François G. Dorais},
date = {2010-04-23},
version = {1},
organization = {MathOverflow},
url = {http://mathoverflow.net/a/22350},
urldate = {2014-04-19},
}


Since MathOverflow user names and titles may contain special characters, use the package inputenc with option utf8 before using the biblatex package in the document preamble, or manually replace special characters by appropriate encoding (e.g. ç by {\c c}). (Also consider using Biber instead of BibTeX as a backend.)

The nameaddon field is not used by standard bibliographic styles but that is what it is used for in styles that do use it; a note field could be used with similar effect with greater compatibility.

Sample output for the entry above:

With biblatex options backend=biber,style=authoryear.

• I think it is not optimal to use the title of the question as "title" for an answer to a question (I know it is like this since a long time but I just happened to notice recently and this seems a good place ot record this opinion). I would rather use something like "Answer to 'Title of the question' by OP of Q" (or possibly without the by OP of Q). This could be analogous to things sometimes used in journals when somebody writes a comment or remark or an appendix or something to some other paper. – user9072 Apr 19 '14 at 13:10
• @quid: titleaddon = {(answer)} would also work. – François G. Dorais Apr 19 '14 at 13:11
• I do not have much opinion on how things are done precisely, especially as I do not oversee the technical details. My only concern is that questions and answers are distinguished in some way. – user9072 Apr 19 '14 at 23:48
• The author field should be {Dorais, François G.}, to ensure proper collation. Now, another question is "what if the author's username is Bugs Bunny". – Federico Poloni Apr 21 '14 at 17:55
• @FedericoPoloni: Neither biber nor bibtex have problems parsing my name correctly, whichever order it is written. Bugs Bunny should be even easier to parse. – François G. Dorais Apr 21 '14 at 18:18
• Well, frankly, I am hesitant about this solution. Right now, I have a highly functional bibtex workflow, which really works for me in all respects, except that the MO bibtex items are not quite optimal (although I can adjust them adequately by hand). Do I really have to move to a totally separate bib system in order to fix that? I'm sure biblatex is great, but will it work with my editor in the way that I want? Can I install it easily? Will it work with my current files without issue? Isn't there a solution that doesn't require a change to a totally new bibtex package? – Joel David Hamkins Apr 22 '14 at 2:26
• @JoelDavidHamkins: I find using biblatex painless. For all of my recent papers adding \usepackage[style=numeric]{biblatex} in the preamble, removing any \bibliographystyle{...}, and adding \printbibliography before the end of the document just works. You can keep using bibtex as a backend but biber is better. tex.stackexchange.com/questions/5091/… The only drawback to biblatex is that some publishers have yet to adapt their house styles to work with biblatex, but that's really their problem in the end... – François G. Dorais Apr 22 '14 at 9:21
• Regarding creating bibtex style files (.bst files) with a MO entry type or even just custom MO fields, that is possible but the custom entries would be simply be ignored when not using the MO house style. So we're stuck with @misc entries, standard fields, and some relatively common fields. Unfortunately, because of they are used for miscellaneous things, most bibliographic styles don't process these entries very well and they often disagree on the usage of common fields. [...] – François G. Dorais Apr 22 '14 at 10:39
• [...] In the end, it's impossible for MO to output a @misc entry that fits all styles. Users will have to keep adjusting the MO entries to fit the bibtex style file they want to use... – François G. Dorais Apr 22 '14 at 10:39
• @Joel: Is your bib system anything like this bib system? – Asaf Karagila Apr 22 '14 at 12:06

I am using a nonstandard citation format, primarily for simplicity. An example is:

MathOverflow Questions (Number refers to URL, so 37679 expands to "http:// mathoverflow.net/questions/37679") [Note: the current display scripts replace the URL with a visible title and hidden link: I've added a space to break this feature. My actual example would not have the space.]

88323 Analogues of Jacobsthal's Function.

56099 Lower bound of the number of relatively primes (each other) in an interval.

68351 Least Prime Factor in a sequence of 2n consecutive integers.

Since I am not interested in making changes when URLs change or databases change, I prefer to provide a simple recipe for translation to avoid as few broken links as possible. I also let the user grab the date from the paper or its metadata, so they can provide their context.

If I were to improve upon this, I might add something like "at this writing 2014.03", as well as provide links to specific versions of the post as suggested by quid. I would refrain from referring to something more specific than the post and its answers; if I had to, I would craft a similar recipe, such as:(Number;version refers to URL, so 37679;38690/1 refers to https://mathoverflow.net/revisions/37679/38690/1). The rationale for this is to give a simple recipe that works at the time the document was publicized, and let the future researcher modify the recipe as needed to resolve the references. If I have to change anything, I only need to change the recipe, not all of its occurrences, unless the question numbering changes.

Gerhard "Prefers Simplicity, Replicability Over Ultra-convenience" Paseman, 2014.04.17

• Indeed, just about everything about a MathOverflow post is changeable: title, URL, user names, etc. I would include the most static and minimal information possible in the reference, and nearby indicate how it resolved at the time I wrote the document. If Pietro Majer changes his name or user number, I don't want to have to update because of that. The title, question number, and URL seem to be the most static and minimal pieces of information needed; I leave the rest to the ingenuity of the future researcher. Gerhard "Will ASCII Exist In 2100?" Paseman, 2014.04.17 – Gerhard Paseman Apr 17 '14 at 21:40